Hello all. I'm hoping to get some help solving some issues with my "new-to-me" 2001 Porsche Boxster S 6-spd manual. I purchased the car in December of 2019 with 52,500 miles on the original engine and it ran perfectly until early November 2020. The car now has 56,980 miles on it. The issues began with a momentary perceived lack of power while merging onto a major highway shifting into 3rd gear and a check engine light later that same day. I purchased the Durametric tool and read a P1126 code, no others. The car wasn't acting up significantly until I cleared the P1126 code. Once I cleared the code, the engine began to idle poorly while cold and would backfire into the intake manifold when pressing the gas pedal, especially a sharp rev.
For reference, when cold, the engine has a tendency to perform much like the engine in this video around the 8 minute and 55second to 9 minute mark:
https://www.youtube.com/watch?v=hddx5Ux1v4Y
It has not stalled on me, even when backfiring into intake etc. Once warmed up, the engine still hesitates going back on the throttle following shifts, but idles well and runs smoothly above 3,000 rpms. Fuel economy is terrible, I'd estimate at 12-15 mpg. Previous to these issues, fuel economy was over 20 mpg.
I got to work:
1. Removed and cleaned the MAF sensor with CRC MAF sensor cleaner. Cleaned/dried thoroughly twice -
NO CHANGE
2. Replaced the air filter and removed the connector to the MAF and drove the car -
NO CHANGE
-assuming this means good MAF, also when warmed up MAF data from Durametric matches Spec (15-16 kg/h at idle) with MAF connector installed
3. Dug into intake manifold, removing the throttle body, plenum and resonance tube and cleaned thoroughly and reassembled -
NO CHANGE
- very little to no oil in intake. AOS tubes in good shape. Oil fill tube outside coated in oil and dust but no visible cracks. Cleaned the tube for reinspection at a later date.
4. Smoked the intake using a smoke machine, finding no smoke emitting from the intake -
NO CHANGE
-smoked long enough for smoke to stream from the oil fill port when I removed the cap
5. Ran a full bottle of Techron fuel system cleaner in a full tank of gas. - NO CHANGE
6. Removed fuel filter and tested the fuel pump flow rate using the steps in the Bentley manual. Pump flowed 1.25 L in 30 seconds (exceeding spec 850mL in 30 sec) -
NO CHANGE
7. Replaced what looked like the original fuel filter and tested the fuel pressure at the fuel rail. 3.8 bar with engine off and 3.3 bar with the engine at idle, meeting specifications in the Bentley manual -
NO CHANGE
8. Tested vacuum at the oil filler with a manometer. With engine fully heat soaked, read between 4.95 and 5.05 inches of water column, meeting specifications I've found online. -
NO CHANGE
9. I've purchased new fuel injectors and fuel pressure regulator and will replace the original fuel injectors (along with pressure regulator while the fuel rail is out) when the weather improves so I do not crack the plastic window (I do all work in unconditioned garage or outside).
The car leaks no fluids. I replaced the water pump, thermostat and coolant in May 2020. Spark plugs were replaced in June 2020, coils in excellent shape, not replaced. Spark plug electrodes were worn, but the plugs were not fouled. I changed the oil & filter at the 6 month mark with 2,900 miles on the oil.
Only knowns worth mentioning:
1. Original clutch, original IMS (at least no records indicating otherwise). Planning clutch/IMS when the weather breaks.
2. Camshaft deviation on bank 1 is -8.2 degrees (out of spec: +/-6deg) Still doing research but considering an engine out when I do the clutch to replace cam wear pads as well as chain tensioner. Bank 2 in spec at -4deg. Dropped oil pan when I bought the car, a few specks (maybe 15, size of ball point) of dark brown plastic in there. Have monitored since and no additional plastic in the oil or filter. Have 6 oil changes (back to 43,000 mi) worth of UOA's and all are good; 2 from me and 4 from P.O. (yes, I know this doesn't mean anything other than "so far, lucky")
I have driven the car 250 miles total throughout all of the steps listed above. I have captured data from durametric while driving on 3 separate occassions. I captured RPM, Banks 1&2 FRA & RKAT, banks 1&2 pre-cat O2 sensor & post-cat O2 sensor voltage, MAF hot film and voltage and intake air temperature if anyone is willing to dig into it. The only data I'd call "suspect" that I captured would be the post-cat O2 sensors, which appear to change while driving (voltage moves up and down) but they remain steady at ~0.74 mV on both banks at idle. The RKAT values shift from 0 to -2.4 on both banks and FRA shifts from 0 to 1.3 on both banks throughout the data acquisition period (I reset the ECU to clear the values and watch them change as I drove the car over time).
I've also actuated both bank Variocam at idle using the Durametric and I can verify that they are both functioning properly, causing the sound/feel of engine to change noticeably when activated.
I'm hoping for some experiences as I know this code and these symptoms are not rare. I've read every forum post I could find and I've tried to follow the troubleshooting steps in those posts, but I'm not getting any success. I've attempted to be succint and demonstrate my version of a methodical approach to troubleshooting the issues. I'm willing to try additional troubleshooting steps and procedures and answer questions as time permits. Thank you for your time!
Best Regards,
Rich
P.S. - should I post to other forums as well and if so, which?
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